But a casual glance at the map convinced many people that our procedure was a mistake. And most newspaper readers in those days were giving much attention to this map. Many periodicals, published in Great Britain and the United States, were fond of exhibiting to their readers diagrams of the North Sea; these diagrams contained one heavy black bar drawn across the Straits of Dover and another drawn across the northern passage from Scotland to Norway. The accompanying printed matter informed the public that these pictures illustrated the one effective "answer" to the submarine. The black bars of printer's ink represented barrages of mines and nets, which, if they were once laid between the indicated spots, would blow to pieces any submarine which attempted to force a way across. Not a single German U-boat could therefore succeed in getting out of the North Sea. All the trans-Atlantic ships which contained the food supplies and war materials so essential to Allied success would thus be able to land on the west coast of England and France; the submarine menace would automatically disappear and the war on the sea would be won. Unfortunately, it was not only the pictorial artists employed on newspapers and magazines who insisted that this was the royal road to success. Plenty of naval men, in the United States and in Europe, were constantly advancing the contention, and statesmen in our own country and in Allied countries were similarly fascinated by this programme. When I arrived in London, in April, 1917, the great plan of confining the submarines to their bases was everywhere a lively topic of discussion. There was not a London club in which the Admiralty was not denounced for its stupidity in not adopting such a perfectly obvious plan. The way to destroy a swarm of hornets--such was the favourite simile--was to annihilate them in their nests, and not to hunt and attack them, one by one, after they had escaped into the open. What the situation needed was not a long and wearisome campaign, involving unlimited new construction to offset the increasing losses of life and shipping, and altogether too probable defeat in the end, but a swift and terrible blow which would end the submarine menace overnight.